Effects of migration and vaccination on the spread and control of yellow fever in Latin American communities: a mathematical modelling study

BACKGROUND: With the COVID-19 pandemic, the stigmatisation of migrants as mere vectors of diseases has worsened. Our goal was to assess how migration rates could affect yellow fever dynamics in Latin American communities, one of those being in Necoclí, Colombia, with 70 000 inhabitants and another 70 000 migrants annually waiting to access central America. METHODS: This modelling study used a susceptible, exposed, infective, recovered, and vaccinated compartimental deterministic model for humans and vectors and numerical simulations applied to three scenarios: (1) migration from an endemic community to a disease-free host community; (2) migration from an endemic community located in a migratory route to a disease-free community; and (3) Necoclí as a case study, evaluating the effects of vaccinating migrants upon arrival. FINDINGS: The type of vector and vaccination coverage in the host community were more relevant for the occurrence of outbreaks than migration rates, and effective vaccinations were able to reduce 55·68% of cases and 54·54% of deaths, but not eliminate them entirely because of the influx of exogenous cases. In Necolcí, assuming the number of migrants equals the resident population, the loss of herd immunity reached 50% every year, and in the case of an outbreak, there were from 3500 to almost 8000 cases of yellow fever in the city. INTERPRETATION: Although migration brings a virus to a community, it does not cause the outbreak outcomes. Therefore, as our results showed, the focus should be on vaccinations and working on vector control rather than blaming migrants. Vaccination could prevent even more cases if any proportion of migrants are already immune, but there are no reliable data on the proportion of vaccinated migrants and no expectation that people on the move will have their personal vaccination documentation on hand. With the increase in the migration of children younger than 5 years, there are increasing concerns about their vaccination history. This model represents many communities in Latin America and suggests that safe migration corridors can substantially contribute to the control of vaccine preventable diseases. FUNDING: Coordination for the Improvement of Higher Education Personnel.